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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

112

SULPHUR

stirring.   The precipitate is collected on a double filter, washed, dried, ignited
and weighed as usual.1   BaS04 X 0-1374 = S.

2. Crude Sulphur.

Crude sulphur is examined for the presence of bitumen, while the mois-
ture and sulphur are detei mined.

In order to obtain a representative sample, each of a, number of the
loaves or lumps is 'broken into o'-8 parts and from each part a, slice cut from
top to bottom, so that the proportions of sulphur, bitumen a.nd extraneous
substances are maintained in each slice. This is of great importance, for
loaves containing so-called oil or metal (veining or brown layers) or adul-
terated with earthy matter. I'Vom 5 to 1,0 kilos are taken, pulverised and
passed through a silk sieve, the coarser particles being re-ground and again
sieved until the whole is in fine powder, which is thoroughly mixed.

1.  Bitumen .---A little of the sample is heated in a tube and any car-
bonaceous residue noted.    Another way is to dissolve the .sample in carbon
disulphide and allow the filtered liquid to evaporate spontaneously in a
small crystallising dish. :  in presence of bitumen, a, brownish or dark brown
border forms on the walls of the vessel and when all the solvent vanishes,
crystals of sulphur remain with brown tufts at. the salient points.

2.  .Determination of the Moisture.   -5 grams of the sample are healed
in a tared porcelain dish at TOO" in a, steam-oven for r 2 hours (according to
some, at: 70-80" for i  hour), the loss representing moisture.

3.  Determination of the Sulphur.   The dried sulphur is next care-
fully heated until the sulphur is completely evaporated, (he loss then giving
the sulphur.    If the sample contains bitumen, the sulphur must be deter-
mined by the method described  for mineral, sulphur.

These methods may be applied directly to good sulphurs which leave
only traces of residue on ignition, but where appreciable mineral residue
remains, the residue from the carbon disulphide extraction is employed.

3, Refined Sulphur (loaves or powder)

In re-fined sulphur in loaves or powder (ground, winnowed) the residue
on calcination is determined to cheek the purity. Wilh sulphur ground
and sifted for agricultural purposes, the degree of fineness must be deter-
mined.

Determination of the Degree of Fineness.-.....This is effected by

Chancel's so-called S'ltlphurimclw or ^'ii'//>/iiinmc/c>', which consists of a,
glass tube, with a, ground stopper : the tube is 230 mm. long and is graduated
from o to too for a space corresponding exactly willi 45 c.c. at 17-5". The

1 To eliminate possible errors due to impurities in the reagents and to allow for
the filter-ash, a blank determination may be carried out as follows : 25 e.e. uf the nitric
acid (D =B 1-52) and 5 drops of bromine, diluted with a little water, are evaporated
almost to dryness on a water-bath, the, whole of the nitric, acid being impelled by
evaporating twice with cone, hydrochloric acid. The residue is taken up in water,
a little barium chloride added and the liquid again evaporated almost to dryucss, filtered
through a double filter, the latter washed with hot water, dried, ashed and weighed.
The weight of this residue is subtracted from that of the barium sulphate obtained in
the actual determination of the sulphur.ution = 0-005 gram Na2S.